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OF    ILLINOIS 


630.7 


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NON  CIRCULATING 

CHECK  FOR  UNBOUND 
CIRCULATING  COPY 


UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  309 


EXPERIMENTS  IN  THE  CULTURE  AND 
FORCING  OF  WITLOOF  CHICORY 

(FRENCH  ENDIVE) 


BY  C.  B.  SAYRE 


URBANA,  ILLINOIS,  MAY,  1928 


SUMMARY 

Witloof  chicory,  known  on  the  market  as  "French  endive,"  is  a 
high-priced  salad  plant,  large  quantities  of  which  are  imported  from 
Belgium  and  France.  Since  this  plant  can  be  grown  successfully  in 
Illinois  and  forced  thruout  the  winter  months,  it  should  prove  of 
special  interest  to  home  gardeners  as  well  as  to  commercial  growers. 

In  these  experiments  Witloof  chicory  was  grown  and  forced  at 
Urbana,  Illinois  for  four  years,  both  indoor  and  outdoor  methods  be- 
ing used.  Attempts  to  force  the  roots  in  the  field  without  removing 
them  from  the  place  where  they  were  grown  were  successful  in  pro- 
ducing a  marketable  crop,  but  the  special  care  required  to  keep  the 
roots  from  freezing  before  they  were  forced  and  the  disproportionate 
amount  of  labor  involved  made  this  method  impractical. 

Planting  the  seed  about  June  15  outdoors  produced  the  largest 
proportion  of  roots  of  best  forcing  size.  The  large  roots  resulting 
from  the  planting  made  in  May  produced-  many  compound  heads 
which  were  unmarketable,  and  small  roots  from  the  July  plantings 
produced  light  yields. 

Equally  good  crops  were  obtained  from  roots  dug  while  in  an 
active  growing  condition  and  forced  immediately,  from  roots  dug  and 
forced  as  soon  as  growth  had  ceased  in  the  fall,  and  from  roots  held 
dormant  in  storage  before  being  forced. 

A  temperature  between  28°  and  45°  F.  was  satisfactory  for  storing 
the  roots.  When  stored  over  five  months  there  was  a  tendency  for 
seed  stalks  to  develop  instead  of  heads  during  the  forcing  of  the  roots. 
Freezing  killed  the  roots. 

Choice  chicory  heads  were  obtained  when  the  roots  were  bedded 
in  brown  silt  loam  in  boxes  with  an  8-inch  covering  of  sand  and  kept 
at  a  temperature  of  about  70°  F.  Lower  temperatures  resulted  in  slow 
growth,  while  temperatures  above  80°  F.  were  likely  to  induce  rot. 
Other  coverings  used  were  sawdust,  sandy  soil,  and  muck,  all  of  which 
proved  inferior  to  sand  as  a  material  thru  which  to  force  growth. 


EXPERIMENTS  IN  THE  CULTURE  AND 
FORCING  OF  WITLOOF  CHICORY 

By  CHARLES  B.  SAYRE,  Formerly  Assistant  Chief  in  Olericulture 

INTRODUCTION 

Witloof  chicory  is  known  in  this  country  principally  from  its  use 
as  a  high-priced  fancy  salad  served  in  the  big  hotels  and  cafes  under 
the  name  of  "French  endive."  Altho  little  known  in  this  country,  it 
has  been  grown  for  centuries  in  Europe.  Large  quantities  are  pro- 
duced in  Belgium  and  France,  particularly  in  the  vicinity  of  Brussels 
and  Paris,  and  it  is  from  this  region  that  most  of  the  supply  for  the 
American  market  is  imported. 

Thus  far  the  demand  for  Witloof  chicory  has  been  principally  in 
the  larger  markets ;  but  there  seems  to  be  a  good  opportunity  for  ex- 
panding the  demand  as  the  crop  becomes  better  known.  Many  mar- 
kets depend  upon  the  imported  product  and  are  inadequately  supplied. 
The  crop  is  grown  to  a  limited  extent  in  New  York,  New  Jersey,  and 
Pennsylvania.  A  few  Illinois  growers  are  producing  it  successfully, 
but  not  in  sufficient  quantities  to  supply  the  demand. 

This  delicious  salad  plant  would  doubtless  find  a  greater  place  in 
home  gardens  also  if  the  ease  with  which  it  can  be  produced  were 
more  generally  realized.  The  fact  is  that  it  can  be  grown  in  home 
gardens  and  the  roots  forced  in  the  winter  with  greater  assurance  of 
success  and  less  care  and  expense  than  are  required  for  many  other 
salad  crops,  such  for  instance  as  head  lettuce.  Grown  in  this  way,  it 
produces  a  fresh,  crisp  salad  thruout  the  winter  months  when  other 
fresh  vegetables  are  unavailable.  Home  gardeners  who  take  pride  in 
extra-fancy  products  will  find  especial  pleasure  in  growing  for  their 
own  tables  this  delicious  salad  crop  which  is  served  as  a  delicacy  in 
exclusive  restaurants  and  clubs. 

Best  Varieties  for  Forcing 

There  are  several  varieties  of  chicory  and  it  is  important  to  secure 
the  true  Witloof  chicory  for  forcing.  Botanically  it  belongs  to  the 
species  Cichorium  intybus  Linn.  It  is  closely  related  to  and  some- 
times confused  with  the  species  Cichorium  endivia  Linn.,  which  in- 
cludes the  common  garden  endive.  The  two  species  are  distinct,  how- 
ever, and  it  is  important  that  their  differences  be  recognized  if  one  is 
to  be  sure  to  secure  the  correct  species  and  variety  for  forcing.  Con- 
fusion is  often  caused  by  the  fact  that  Witloof  chicory  is  known  on 
the  market  almost  exclusively  by  the  term  French  endive,  and  many 
seed  catalogs  are  likewise  listing  Witloof  chicory  by  the  incorrect  term 
French  endive. 

443 


444  BULLETIN  No.  309  [May, 

Of  the  species  Cichorium  intybus  Linn.,  there  are  several  varieties 
in  commerce.  Likewise  the  wild  chicory,  a  common  roadside  weed  in 
Illinois,  belongs  to  this  species.  Altho  this  wild  chicory  can  be  forced, 
it  produces  a  small  head  of  very  bitter  flavor. 

The  large-rooted  Brunswick  is  a  commercial  variety  which  has 
very  deeply  cut  leaves  divided  somewhat  like  those  of  a  dandelion  and 
spread  horizontally.  With  this  spreading  habit  of  growth  it  produces 
a  loose,  spreading  head,  and  consequently  is  not  desirable  for  forcing. 


FIG.  1. — A  PLANT  OF  TRUE  WITLOOF  CHICORY 

Note  the  wide,  smooth  leaves,  thick  midrib, 
and  erect  habit,  which  is  typical  of  the  growth 
of  the  plant  in  the  field. 

This  variety  is  grown  principally  for  its  large  roots,  which  are  sliced, 
roasted,  and  ground  and  used  as  a  coffee  substitute.  Another  large- 
rooted  variety  used  principally  as  a  coffee  substitute  is  the  Magde- 
burg. This  has  smooth-edged  leaves  which  stand  erect,  thus  making  it 
suitable  for  forcing,  particularly  to  form  what  is  known  as  barbe-de- 
capucin.  To  produce  barbe-de-capucin  the  roots  are  forced  in  a  dark 


1928} 


CULTURE  AND  FORCING  OF  WITLOOF  CHICORY 


445 


place  without  confining  the  tops.  A  loose-headed  top  develops,  com- 
posed of  long,  slender,  blanched  leaves  as  shown  at  A,  Fig.  4,  page  448. 
Any  of  the  varieties  may  be  used  to  produce  barbe-de-capucin  but  the 
improved  varieties  such  as  Magdeburg  and  Witloof  are  sweeter  and 
less  bitter. 

The  true  Witloof  variety  is  said  to  be  a  selection  of  the  Magde- 
burg, but  it  is  characterized  by  wider,  smoother-edged  leaves,  with 


FIG.  2. — CHICORY  GROWING  IN  FORCING  BOXES 
The  above  growth  is  characteristic  of  the 
compact,  firmly  closed,  well-blanched  heads  pro- 
duced under  proper  forcing  conditions.  This 
shows  a  section  thru  the  forcing  box  after  the 
sand  thru  which  the  heads  have  grown  has  been 
removed.  For  home  use  boxes  like  this  holding 
about  two  dozen  heads  each  are  satisfactory. 

wider,  thicker  midribs,  and  a  more  erect  habit  of  growth.  These 
characteristics  make  it  specially  suitable  for  forcing,  since  they  result 
in  a  blanched  head  which  is  more  compact  and  solid  and  less  bitter 
than  other  varieties. 


446 


BULLETIN  No.  309 


Methods  of  Forcing 


[May, 


Practices  in  the  forcing  of  this  crop  differ  slightly,  but  commercial 
and  home  gardeners  all  follow  the  same  principles.  In  general,  the  ma- 
ture roots  are  transplanted  to  a  compact  space  (boxes)  where  the  tem- 
perature can  be  controlled.  A  layer  of  sand  about  8  inches  deep  is 
then  filled  in  above  the  crowns  and  the  growth  is  forced  thru  this  sand. 
The  weight  of  the  sand  causes  the  shoots  to  develop  into  a  firmly 
closed,  compact  head,  which  is  blanched  to  a  creamy  white  as  shown 
at  B,  Fig.  4.  As  soon  as  the  tips  of  the  shoots  appear  at  the  surface 
of  the  covering  layer  of  sand,  the  heads  are  ready  to  harvest.  Fig.  2 
shows  the  characteristic  growth  obtained  under  forcing  conditions.  If 
allowed  to  grow  in  the  light,  the  leaves  turn  green  and  become  bitter. 

For  home  use  a  box  (Fig.  2)  that  will  hold  about  two  dozen  roots 
and  is  sufficiently  deep  for  the  8-inch  layer  of  sand,  makes  a  satis- 


FIG.  3. — AN  INEXPENSIVE  FORCING  SHED 
The  roots  are  bedded  vertically  on  the  floor 
in  shallow  bins  or  beds,  and  sand  or  light  soil  is 
filled  in  above  the  crowns.  The  beds  may  be 
covered  with  a  deep  layer  of  straw  or  the  shed 
may  be  heated,  to  forcing  temperature. 


factory  place  in  which  to  force  this  crop.  Two  or  three  boxes  started 
at  intervals  of  a  week  or  ten  days  will  maintain  a  constant  supply 
for  home  use.  The  boxes  may  be  placed  in  the  basement  during  the 
forcing  period. 

In  forcing  on  a  commercial  scale,  large  beds  may  be  used  on  the 
cellar  floor  or  in  a  root  cellar,  or  under  greenhouse  benches. 

Inexpensive  sheds  may  also  be  used  for  forcing  the  crop.  In  this 
case  the  roots  are  bedded  vertically  on  the  floor  of  the  shed  in  shallow 
bins  or  beds.  Sand  or  light  soil  is  then  filled  in  above  the  crowns,  as 
shown  in  Fig.  3.  The  beds,  then,  may  be  covered  with  a  deep  layer 
of  straw  or  the  shed  may  be  heated  to  the  forcing  temperature. 

Another  method  is  to  force  the  roots  in  outdoor  trenches  or  beds. 
A  modification  of  this  plan  is  to  force  the  roots  right  in  the  row  where 


1928]  CULTURE  AND  FORCING  OF  WITLOOF  CHICORY  447 

they  have  grown.    This  was  done  as  part  of  the  work  in  this  experi- 
ment and  the  method  was  discarded  as  impractical  (see  page  459). 

For  the  market  the  heads  should  be  carefully  cleaned  and  graded 
and  packed  in  paper-lined  boxes  or  baskets  holding  about  ten  pounds 
each.  One  large  grower  uses  boxes  measuring  5  by  11  by  18  inches, 
which  hold  14  to  15  pounds  when  packed.  Retailers  prefer  small  pack- 
ages and  can  handle  the  crop  to  better  advantage  in  small  lots. 

Object  of  These  Experiments 

The  object  of  these  experiments  was  to  secure  information  in  re- 
gard to  the  best  methods  of  producing  Witloof  chicory  in  Illinois.  The 
points  specifically  studied  were  the  following: 

1.  The  best  time  to  plant  seed  from  which  to  grow  roots  for  forcing. 

2.  The  advantages,  if  any,  of  a  rest  period  for  the  roots  before  they  are 

forced. 

3.  The  effect  of  freezing  the  roots  before  forcing  them. 

4.  The  best  method  of  storing  the  roots  for  forcing  late  in  the  winter  or 

spring. 

5.  The  best  temperature  for  forcing  the  roots. 

6.  The  best  size  of  roots  for  forcing. 

7.  The  practicability  of  growing  more  than  one  crop  from  the  same  roots. 

8.  The  practicability  of  forcing  the  roots  in  the  field  without  removing  them 

from  the  row. 

9.  The  difference  in  the  growth  produced  when  the  roots  are  forced  thru 

sand  and  when  forced  thru  other  materials. 

CONDITIONS  OF  EXPERIMENT 
Planting  of  Seed  and  Care  of  Roots 

In  these  tests  Witloof  chicory  was  grown  in  the  experimental 
gardens  of  the  Department  of  Horticulture  at  Urbana  during  the  sea- 
sons 1921  to  1924  inclusive,  and  the  roots  were  forced  during  the  fol- 
lowing winters. 

The  seed  was  sown  on  various  dates  from  May  to  July  on  a  brown 
silt  loam  soil  in  rows  3  feet  apart,  thus  allowing  for  horse  cultivation. 
The  seedlings  were  thinned  to  about  6  inches  apart  in  the  row. 

Cultivation. — The  plants  were  given  ordinary  cultivation  thru  the 
growing  season,  and  each  year  the  roots  were  dug  late  in  October  or 
November.  The  tops  were  cut  off  at  the  time  the  roots  were  dug. 
After  experience  gained  the  first  season,  when  some  of  the  tops  were 
cut  too  short,  an  effort  was  made  to  cut  off  the  tops  about  2  inches 
above  the  crown.  These  were  removed  with  a  single  stroke  of  a  butcher 
knife.  Likewise,  after  the  first  season  all  overgrown  roots  (over  2% 
inches  in  diameter)  and  all  roots  that  had  produced  seed  stalks  were 
discarded  at  digging  time. 

Forcing  Boxes. — All  of  the  roots  except  those  forced  in  trenches 
were  forced  in  boxes.  These  boxes  were  of  various  sizes  but  of  suffi- 


448 


BULLETIN  No.  309 


[May, 


cient  height  so  that  after  the  roots  were  bedded  vertically  in  soil  in 
the  boxes,  8  inches  of  sand  could  be  filled  in  above  the  crowns. 

Experience  showed  that  the  boxes  must  be  substantially  built; 
otherwise  the  side  pressure  of  the  sand  causes  the  sides  to  bulge  or 
break.  A  box  20  inches  high,  12  inches  wide,  and  16  inches  deep, 
inside  measurements,  is  about  as  large  as  can  be  handled  conveniently 
in  pouring  off  the  sand  when  a  crop  is  ready  to  harvest.  One  of  this 
size  holds  about  30  roots.  Fig.  2  shows  one  of  the  forcing  boxes  with 
the  side  removed  and  the  sand  poured  off  when  a  crop  was  ready  to 
harvest.  The  long  tips  of  the  roots  are  of  no  value  in  forcing.  Con- 
sequently these  were  cut  off,  making  the  roots  a  uniform  length  of  8 
inches.  In  bedding  the  roots,  they  were  placed  vertically  about  an 


FIG.  4. — TYPICAL  SPECIMENS  OF  THE  FORCED  PRODUCT  OF 

WITLOOF  CHICORY 

(A)  Loose  head  and  long  slender  leaves  known  as  barbe-de- 
capucin  produced  by  forcing  the  roots  in  darkness  without  a  cover- 
ing layer  of  sand  above  the  crowns;  (B)  extra  fancy  grade,  -called 
French  endive  on  the  market;  (C)  No.  1  market  grade;  (D)  too 
small  for  market  but  good  for  home  use. 

inch  apart,  with  the  crowns  at  the  same  level  and  with  soil  filled  in 
around  them  to  the  level  of  the  crowns.  They  were  then  thoroly 
watered. 

Watering. — It  was  found  that  if  the  soil  around  the  roots  is  thoroly 
watered  at  the  time  the  roots  are  bedded,  no  additional  watering  is 
necessary  to  produce  the  crop.  During  the  first  season  the  boxes  were 
watered  at  frequent  intervals  during  the  forcing  period  by  pouring  the 
water  on  the  covering  layer  of  sand.  Considerable  rot  developed  in 
the  heads  growing  up  thru  the  moist  sand.  The  next  season  a  pipe 
was  thrust  thru  the  sand,  and  water  was  poured  into  the  pipe  so  that 
the  water  flowed  out  at  the  level  of  the  soil.  This  reduced  the  amount 


1928]  CULTURE  AND  FORCING  OF  WITLOOF  CHICORY  449 

of  rot.  In  the  next  two  seasons  the  soil  was  thoroly  soaked  at  the 
time  the  roots  were  bedded,  and  no  additional  watering  was  given. 
Sand  was  not  filled  in  above  the  crowns  until  a  day  after  they  had 
been  bedded  and  watered.  This  kept  the  sand  dry  and  practically 
controlled  the  rot. 

Grading  the  Crop 

In  all  of  the  lots  in  which  yield  records  were  taken  the  same 
standards  were  used  in  grading  the  product.  Two  marketable  grades 
were  made,  namely  "extra  fancy,"  and  "No.  1."  The  extra  fancy 
grade  included  only  large,  firm,  well-blanched  heads  of  very  compact 
growth.  The  No.  1  grade  included  heads  that  were  slightly  smaller,  or 
less  compact,  but  which  were  well  blanched  and  free  from  blemish  or 
rot.  Typical  extra  fancy  heads  are  shown  at  B,  Fig.  4,  and  typical 
No.  1  heads  are  shown  at  C,  Fig.  4. 

A  comparison  of  the  average  weight  per  head  of  each  grade  of  the 
different  lots  would  seem  to  indicate  considerable  variation  and  lack 
of  uniformity  in  grading.  However,  the  extra  fancy  heads  in  each  lot 
were  distinctly  superior.  That  is,  the  grading  was  based  on  the  size, 
shape,  and  solidity  of  the  heads  and  represented  definite  standards  in 
appearance,  and  the  grades  were  quite  uniform  between  the  lots. 

It  should  be  noted  in  records  of  yields  that  the  longer  the  forcing 
period  the  greater  was  the  average  weight  per  head.  This  result  might 
naturally  be  expected,  as  the  longer  time  would  give  the  slower  grow- 
ing heads  a  chance  to  fill  out  more  and  raise  the  general  average.  Each 
lot  was  harvested  when  several  shoots  had  grown  thru  the  covering 
layer  of  sand.  In  some  cases  it  was  found  that  a  few  shoots  had 
grown  unusually  fast  and  would  indicate  that  the  lot  was  ready  to 
harvest  when  in  reality  the  majority  of  the  roots  in  the  lot  had  not 
attained  maximum  growth.  Consequently  harvesting  at  this  time  re- 
sulted in  a  lower  average  weight  per  head. 

RESULTS  OBTAINED 
June  15  Best  Planting  Time 

The  time  of  planting  the  seeds  to  grow  roots  for  forcing  is  of 
considerable  importance.  If  the  seed  is  sown  too  early  it  will  result 
in  the  development  of  a  large  percentage  of  overgrown  roots  that 
produce  seed  stalks  or  compound  heads.  Roots  of  this  type  are  worth- 
less for  forcing.  On  the  other  hand,  if  the  seed  is  sown  too  late  in  the 
season,  the  roots  will  be  too  small  to  develop  a  maximum  forcing  crop. 

The  best  time  for  planting  was  determined  by  the  growth  at 
digging  time.  Each  season  as  the  roots  were  dug,  a  representative 
portion  of  a  row  was  critically  examined,  the  size  and  maturity  of  200 
"field  run"  roots  was  noted,  and  the  percentage  of  desirable  and  of 
worthless  roots  recorded.  The  results  showed  that  planting  the  seed 


450 


BULLETIN  No.  309 


[May, 


about  June  15,  which  gave  about  a  four  months'  growing  period,  pro- 
duced the  largest  proportion  of  roots  of  best  forcing  size  and  a  low 
percentage  of  seed  stalks  (Table  1).  Planting  in  May  resulted  in  a 
large  proportion  of  overgrown  roots  and  the  development  of  seed 
stalks;  and  planting  in  July  resulted  in  a  larger  proportion  of  small 
roots.  This  is  in  accordance  with  the  experience  of  most  growers  in 
this  region  and  in  the  East,  the  majority  of  whom  recommend  planting 
about  June  15. 

Rest  Period  of  No  Advantage 

To  determine  whether  or  not  a  rest  period  is  necessary  before  the 
roots  can  be  forced  satisfactorily,  50  medium-sized  roots  were  dug 
from  the  field  on  October  2  and  again  on  October  16,  while  they  were 

TABLE  1. — WITLOOF  CHICORY:  RELATION  OP  PLANTING  DATE  To 

SIZE  OP  ROOTS  PRODUCED1 

(200  roots  examined  for  each  planting  date) 


Planting  date 

Under- 
sized 
roots: 
less  than 
1  inch 

Medium- 
sized 
1  to  \% 
inches 

Large 
roots: 

1%  to  2% 
inches 

Overgrown 
roots: 
over  2% 
inches 

Seed  stalks 

May  15,  1921  

perct. 
13 
19 
23 

(Less   than 
%  inch) 
14 

19 

perct. 
34 
49 

44 

(%  to  2 

6 

(%  to  I3/ 

4 

perct. 
37 
23 
27 

inches) 

r 

inches) 
I 

perct. 
16 
9 
6 

(Over  2 
inches) 
19 

(Over  1% 
inches) 
33 

perct. 
22 
14 
11 

3 

1 

June  24,  19222  

July  2,  19232  

June  14,  1924  

July  1,  1924  

during  the  first  three  seasons  these  roots  were  graded  in  four  sizes.  In  the 
last  season  only  three  grades  were  considered,  namely:  (1)  too  small  for  forcing, 
less  than  %  inch)  (2)  good  forcing  size,  %  inch  to  2  inches;  and  (3)  overgrown,  over 
2  inches.  Thru  an  error  the  upper  limit  of  the  good  forcing  size  was  reduced  in  the 
July  planting  in  1924.  Consequently  the  proportionate  amount  of  overgrown  roots 
was  increased.  A  thin  stand  probably  also  increased  the  proportion  of  overgrown 
roots  in  this  planting. 

Irrigated.  It  may  be  assumed  that  irrigation  promoted  growth  and  increased 
the  size  of  the  roots. 

still  in  an  active  growing  condition,  and  were  forced  immediately 
(Lots  19  and  20) .  By  November  10  the  growing  season  was  over  and 
all  roots  were  dug.  Two  lots  (Nos.  21  and  22)  were  stored  at  31°  F. 
for  later  forcing. 

This  test  was  repeated  the  next  season  by  digging  and  imme- 
diately forcing  50  actively  growing  medium-sized  roots  on  October  1 
(Lot  37)  and  a  similar  lot  on  October  15  (Lot  38).  These  were  com- 
pared with  two  lots  (Nos.  39  and  40)  from  the  main  crop  which  was 


1928}  CULTURE  AND  FORCING  OF  WITLOOF  CHICORY  451 

dug  on  November  19  and  kept  dormant  in  cold  storage  for  later  forc- 
ing. 

All  lots  were  forced  in  a  warm  greenhouse.  A  comparison  of  the 
yields  (Table  2)  clearly  shows  that  a  rest  period  is  unnecessary  before 
Witloof  chicory  roots  can  be  forced  successfully.  The  roots  may  be 
taken  from  the  field  in  an  active  growing  condition  and  immediately 
forced,  or  with  equal  success  the  roots  may  be  matured  and  kept  in  a 
dormant  condition  before  forcing.  The  yields  and  the  time  required 
for  forcing  are  approximately  the  same  with  or  without  a  rest  period. 

Roots  that  had  an  extra  long  rest  period,  it  should  be  noted,  had 
a  tendency  to  produce  seed  stalks.  This  is  shown  subsequently  in  Lots 
5  to  8  inclusive. 

Freezing  Fatal  to  Witloof  Chicory  Roots 

Before  some  plants,  such  as  rhubarb,  can  be  forced  successfully 
it  is  first  necessary  to  freeze  the  roots  to  break  the  rest  period.  In 
order  to  determine  whether  or  not  freezing  would  result  in  physiolog- 
ical changes  in  chicory  that  would  stimulate  growth  as  is  the  case  with 
rhubarb,  some  roots  were  subjected  to  freezing  temperatures. 

Fifty  roots  of  the  1921  crop  (Lot  12,  Table  3)  were  covered  with 
soil  and  placed  in  cold  storage  at  a  temperature  of  zero  for  two  weeks. 
When  these  roots  were  removed  from  cold  storage,  they  were  thawed 
out  slowly  in  a  cool  cellar.  As  they  thawed,  they  became  watery  and 
soft  and  it  was  found  that  the  entire  lot  was  killed. 

This  test  was  repeated  with  50  roots  of  the  1924  crop  (Lot  50, 
Table  3).  In  this  case  the  storage  temperature  was  10°  F.  for  two 
weeks.  The  result  was  the  same;  all  the  roots  were  killed  by  the 
freezing. 

Another  lot  of  roots,  Lot  27,  was  not  dug  in  the  fall  (of  1922), 
but  was  left  in  the  field  unprotected  from  freezing.  After  severe 
freezing  weather,  hot  manure  was  heaped  over  the  row  to  force  the 
roots,  but  no  growth  resulted.  A  similar  lot  of  roots  left  in  the  row 
but  protected  from  freezing  (Lot  28,  page  459)  was  forced  successfully 
when  hot  manure  was  heaped  over  the  row.  Furthermore  Lots  9  and 
10,  placed  in  outdoor  trenches  and  mulched  to  protect  them  from 
freezing,  were  forced  successfully  when  hot  manure  was  heaped  over 
the  trench.  Lot  29,  in  an  outdoor  trench  not  protected  from  freezing, 
was  a  total  loss. 

These  results  clearly  indicate  that  freezing  is  fatal  to  Witloof 
chicory  roots. 

Successful  Storage  Requires  Moderate  Temperatures 

In  order  to  extend  the  marketing  period  of  Witloof  chicory  over 
several  months,  it  is  necessary  to  store  the  roots  or  keep  them  in  a 
dormant  condition  until  needed  for  forcing. 


452 


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CULTURE  AND  FORCING  OF  WITLOOF  CHICORY 


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454  BULLETIN  No.  309  [May, 

Various  experiments  were  tried  in  order  to  determine  the  best 
method  of  storing  the  roots  so  that  they  could  be  forced  late  in  the 
season.  In  each  case  the  roots  were  covered  with  soil  to  protect  them 
from  drying  out  or  shriveling.  Several  lots  were  left  for  one  to  five 
months  in  cold  storage  at  31°  F.  Other  lots  were  stored  at  a  temper- 
ature of  45°  F.,  and  one  lot  at  28°  F.  Another  lot  was  left  in  a  cellar 
at  a  temperature  of  about  53°  F.,  and  a  few  lots  were  kept  in  outdoor 
pits  protected  from  freezing.  These  lots  were  all  forced  in  the  warm 
greenhouse  except  the  lots  in  pits,  Lots  9  and  10,  which  were  forced 
outdoors. 

For  convenience  of  comparison,  the  yields  secured  from  roots 
stored  in  various  ways  are  listed  in  Table  3.  These  results  indicate 
that  the  roots  may  be  stored  successfully,  either  in  outdoor  trenches 
or  in  boxes  in  cold  storage,  at  a  temperature  sufficiently  low  to  prevent 
growth,  but  not  low  enough  to  freeze.  Experience  with  Lot  51  indicates 
the  freezing  temperature  of  chicory  roots  is  below  28°  F.,  while  a  tem- 
perature of  10°  F.  is  fatal,  as  shown  in  Lot  50.  That  45°  F.  is  suffi- 
ciently low  to  prevent  growth  is  shown  by  Lot  7 ;  and  that  growth  will 
occur  at  53°  F.  is  shown  by  five  lots,  No.  30  in  Table  3  and  Nos.  13, 
23,  41,  and  53  in  Table  4. 

Because  of  the  satisfactory  results  secured  in  storing  the  roots  at 
31°  F.  and  the  availability  of  storage  space  at  this  temperature  (apple- 
storage  temperature)  all  of  the  remaining  lots,  except  as  otherwise 
noted,  were  so  stored. 

The  fact  that  seed  stalks  developed  in  a  number  of  heads  after 
being  stored  five  months  (Lots  5,  51,  7,  and  30)  would  seem  to  indi- 
cate that  if  the  roots  are  held  in  storage  too  late  in  the  season  they 
attain  an  age  or  stage  of  maturity  following  which  they  are  likely 
to  produce  seed  stalks. 

In  Lot  30,  stored  in  a  cellar  at  about  53°  F.,  growth  started  fol- 
lowed by  rot,  or  at  least  the  old  stubs  rotted  away.  However,  the 
roots  were  plump.  Eighty  small,  slender  heads  were  produced  from 
this  lot,  none  of  which  were  marketable.  The  total  weight  of  the 
heads  was  only  2  pounds  3  ounces,  and  many  of  them  had  seed  stalks 
in  the  center. 

In  Lot  9  the  roots  were  bedded  upright  in  a  trench  outdoors  with 
2  inches  of  sand  above  the  crowns.  As  freezing  weather  came,  a  mulch 
of  old  manure  was  heaped  over  this  trench.  At  the  start  of  the  forcing 
period,  the  old  manure  was  removed  and  hot,  fermenting  manure  was 
heaped  over  the  roots  to  a  depth  of  3  feet.  At  this  time  a  part  of  the 
trench  was  opened  and  it  was  found  that  from  2  to  3  inches  of  growth 
had  occurred  after  the  roots  had  been  placed  in  the  trench.  The  growth 
was  stocky  but  had  one  unfavorable  feature — most  of  the  heads  were 
bending  over  as  tho  turning  back  from  the  cold.  Apparently  they  had 
started  an  upright  growth  and  later  turned  down.  This  peculiar  growth 
did  not  occur  in  Lot  10.  In  that  lot  the  roots  were  bedded  upright  in 


1928}  CULTURE  AND  FORCING  OF  WITLOOP  CHICORY  455 

the  trench  outdoors  and  8  inches  of  sand  filled  in  above  the  crowns; 
this  was  mulched  to  protect  it  from  freezing.  In  both  Lots  9  and  10 
the  forcing  period  was  lengthened  by  the  fact  that  a  cold  wave,  with 
sub-zero  weather,  occurred  shortly  after  the  hot  manure  was  placed 
over  the  trenches  to  start  growth ;  this  cooled  the  manure  and  retarded 
growth. 

In  Lot  29  the  roots  were  bedded  upright  in  a  shallow  trench  and 
only  2  inches  of  sand  was  filled  in  above  the  crowns.  No  effort  was 
made  to  protect  this  lot  from  freezing.  At  the  time  the  hot  manure 
was  heaped  over  the  trench  to  start  the  forcing,  it  was  found  that  the 
roots  were  frozen  in  the  soil.  No  growth  resulted,  the  roots  having 
been  killed  by  the  freezing. 

Roots  Best  Forced  at  About  70°  F. 

In  order  to  determine  the  best  temperature  for  forcing,  roots  which 
had  been  kept  in  cold  storage  for  two  months  at  31°  F.  were  bedded  in 
forcing  boxes  and  placed  in  the  following  temperatures  and  locations: 
(1)  A  basement  having  a  constant  temperature  of  about  53°  F. ;  (2)  a 
cool  greenhouse  having  a  night  temperature  of  about  50°  F.  and  day 
temperatures  of  60°  to  65°  F.;  (3)  a  greenhouse  having  a  night  tem- 
perature of  55°  and  day  temperatures  of  65°  to  70°  F.;  (4)  a  warm 
greenhouse  having  a  night  temperature  of  65°  and  day  temperatures 
of  75°  to  80°  F.;  (5)  a  tunnel  containing  heating  pipes  having  a  con- 
stant temperature  of  85°  to  90°  F.  Medium-sized  roots  were  used  in 
each  case  and  were  forced  in  each  of  these  temperatures  during  the 
four  forcing  seasons  (Table  4). 

In  each  season  the  lot  forced  in  the  warm  greenhouse  (average 
temperature  about  70°  F.)  was  superior  to  the  other  lots,  both  in  per- 
centage of  marketable  heads  and  in  average  weight  of  marketable 
heads;  and  in  all  four  seasons  the  largest  yields  of  marketable  heads 
were  produced  at  this  temperature.  The  results  clearly  indicate,  how- 
ever, that  Witloof  chicory  is  not  very  exacting  in  regard  to  forcing 
temperature  providing  it  is  not  too  high;  85°  F.  or  above  is  too  hot  for 
healthy  growth.  All  lots  forced  at  this  temperature  were  a  total  loss 
because  of  rot.  It  appears  that  the  higher  the  forcing  temperature  the 
larger  is  the  yield,  providing  the  temperature  does  not  exceed  80°  F. 
An  average  temperature  of  about  70°  F.  proved  to  be  the  optimum 
forcing  temperature  in  these  experiments. 

Medium-Sized  Roots  Best  for  Forcing 

To  determine  the  best  size  of  roots  for  forcing,  those  grown  during 
the  first  season  were  graded  into  the  following  sizes  based  on  the 
largest  diameter:  (1)  very  small,  diameter  %  to  %  inch;  (2)  small, 
diameter  %  to  1  inch;  (3)  medium,  diameter  1  to  1%  inches;  (4)  large, 
diameter  1%  to  2%  inches;  (5)  very  large,  diameter  over  2%  inches. 


456 


BULLETIN  No.  309 


[May, 


TABLE  4. — YIELDS  OF  WITLOOF  CHICORY  PRODUCED  AT  DIFFERENT 

FORCING  TEMPERATURES 
(Medium-sized  roots  in  each  lot) 


(1)  Basement:  constant  tem- 
perature 53°  F.    Lots  

1921 
13 

1922 
23 

1923 
41 

1924 
53 

Average 

Percentage  of  market- 
able heads  

72 

56 

60 

68 

64 

Average  weight  of 
marketable  heads, 
ounces  

2.7 

2   a 

3  1 

2  8 

2.8 

Forcing  period,  days 

18 

19 

20 

18 

(2)  Cool  greenhouse:  night 
50°  F.,  day  65°  F.    Lots.  .  . 

14 

24 

42 

54 

Average 

Percentage  of  market- 
able heads  

60 

70 

57 

66 

63 

Average  weight  of 
marketable  heads, 
ounces  

2.6 

2.8 

3.1 

2.9 

2.8 

Forcing  period,  days  .  . 

18 

19 

20 

18 

(3)  Medium  greenhouse: 
night  55°  F.,  day  70°  F. 
Lots  

25 

43 

55 

Average 

Percentage  of  market- 
able heads  

64 

62 

72 

66 

Average  weight  of 
marketable  heads, 
ounces  

2.8 

2.9 

3.1 

2.9 

Forcing  period,  days  .  . 

19 

20 

18 

(4)  Warm  greenhouse:  night 
65°  F.,  day  80°  F.    Lots... 

2 

22 

40 

52 

Average 

Percentage  of  market- 
able heads  

80 

68 

84 

76 

77 

Average  weight  of 
marketable  heads, 
ounces  

3.0 

3.5 

3.1 

3.2 

3.2 

Forcing  period,  days.  . 

18 

19 

20 

18 

(5)  Heating  tunnel:  constant 
temperature  85°  to  90°  F. 
Lots  

15 

26 

44 

56 

Ayerage 

Each  lot  forced  in  the  heating  tunnel  was  a  complete  loss.    Lot  56  made  a 
quick  growth  but  was  a  total  loss  from  rot. 

The  next  two  seasons  the  roots  were  graded  on  the  same  scale, 
except  that  roots  smaller  than  %  inch  in  diameter  or  larger  than  2% 
inches  were  discarded.  The  test  of  comparative  sizes  was  not  con- 
tinued into  the  fourth  season.  For  this  season  all  roots  under  %  inch 
or  over  2  inches  in  diameter  were  discarded  at  digging  time,  as  in  the 
second  and  third  seasons,  and  the  remaining  roots  were  not  sub- 
divided but  were  classed  together  as  one  forcing  grade. 

Roots  of  each  size  were  forced  each  year  both  in  the  cool  and  in 
the  warm  forcing  house- 


1928} 


CULTURE  AND  FORCING  OF  WITLOOF  CHICORY 


457 


The  yields  show  conclusively  that  medium-sized  roots  (1  inch  to 
1%  inches  in  diameter)  are  by  far  the  best  size  for  forcing  (Table  5). 
In  fact  in  each  comparison  each  year,  both  in  the  cold  and  in  the 
warm  temperatures,  the  medium-sized  roots  made  the  best  showing, 
considering  quality  of  heads  as  well  as  weight.  Altho  heavier  total 
yields  were  produced  by  the  large  roots,  most  of  the  weight  was  from 
compound  heads  or  from  large  clumps  of  small  pencil-like  heads  which 
were  unmarketable  (Fig.  5). 


FIG.  5. — TYPICAL  HEADS  PRODUCED  BY  ROOTS  OF  DIFFERENT  SIZES 

(A)  Unmarketable  compound  heads  produced  by  extra  large 
roots;  (B)  extra  fancy  heads  from  medium-sized  roots;  (C)  small 
heads  from  small  roots.  The  head  at  the  extreme  right  is  below 
market  grade. 

In  some  cases  the  small  roots  produced  a  more  marketable  pro- 
duct than  the  large  roots.  In  general,  they  produced  heads  that  were 
firm  and  of  high  quality  but  too  small  for  the  extra  fancy  grade. 

It  should  be  noted  from  Table  5  that  the  yields  produced  by  roots 
of  each  size  were  slightly  heavier  in  the  lots  forced  in  the  warm  house 
than  they  were  in  lots  of  similar  size  forced  in  the  cool  house;  which 
is  further  evidence  of  the  advantage  of  a  temperature  of  about  70°  F. 


458 


BULLETIN  No.  309 


[May, 


TABLE  5. — RELATION  OF  SIZE  OP  WITLOOF  CHICORY  ROOTS  TO 
YIELD  OF  MARKETABLE  HEADS 

(30  roots  in  each  lot) 


Lot 

Size  of  roots 

Extra  fancy 
heads 

No.  1  heads 

Total  market- 
able heads 

Number 

Av.  wt. 

Number 

Av.  wt. 

Number 

Av.  wt. 

Cool  forcing  temperature 


16 

1921 
Small1  

2 

oz. 
3.1 

17 

oz. 
1.8 

19 

oz. 
1.9 

14 

Medium2  

11 

3  4 

7 

1  8 

18 

2.6 

17 

Large3  

10 

3  7 

4 

2  4 

14 

3.4 

18 

Very  large4  

7 

4  3 

2 

2  2 

9 

3.8 

31 

1O99 
1WS1S 

Small  

2 

3  3 

23 

2  0 

25 

2  1 

24 

Medium  

11 

3.4 

10 

2.2 

21 

2.8 

32 

Large.  . 

9 

4.5 

6 

2.3 

15 

3.6 

45 

1923 
Small  

5 

3.2 

17 

1  9 

22 

2.2 

42 

Medium  

12 

3  6 

5 

1  8 

17 

3.1 

46 

Large  

10 

3  5 

3 

2  1 

13 

3.2 

Warm  forcing  temperature 


6 

1921 
Small  

4 

3.2 

17 

2.1 

21 

2.3 

2 

Medium  

15 

3.6 

9 

2.1 

24 

3.0 

8 

Large  

11 

4  0 

3 

2.0 

14 

3.6 

11 

Very  Large  

7 

3  6 

3 

2.2 

10 

3.2 

33 

1922 
Small  

0 

0 

20 

2.2 

20 

2.2 

34 

Medium  

17 

3.9 

7 

2.3 

24 

3.4 

35 

Large  

9 

4.1 

4 

2.2 

13 

3.5 

47 

1923 
Small  

2 

3.4 

17 

2.2 

19 

2.3 

48 

Medium  

18 

3.9 

8 

2.4 

26 

3.4 

49 

Large  

9 

4.1 

2 

2.2 

11 

3.8 

^mall  roots:  %  to  1  inch  maximum  diameter. 
2Medium  roots:  1  to  1%  inches  maximum  diameter. 
3Large  roots:  1%  to  2%  inches  maximum  diameter. 
4Very  large  roots:  over  2%  inches  maximum  diameter. 

Roots  Cannot  Be  Forced  Successfully  a  Second  Time 

In  producing  one  head  of  Witloof  chicory  under  forcing  conditions, 
the  food  material  stored  in  the  root  is  not  nearly  exhausted.  An  effort 
was  made,  therefore,  to  use  this  remaining  food  material  to  produce 
additional  yields,  but  the  tests  clearly  indicate  that  a  second  crop  of 
marketable  heads  cannot  be  produced  from  the  same  roots. 


1928}  CULTURE  AND  FORCING  OF  WITLOOF  CHICORY  459 

In  Lots  3  and  21,  each  of  which  included  30  medium-sized  roots, 
the  heads  were  cut  about  half  an  inch  above  the  crown  when  the  first 
crop  was  harvested.  This  was  done  so  as  to  avoid  injuring  the  central 
bud.  The  heads  cut  in  this  manner,  however,  fell  apart  readily  and 
could  not  be  marketed  satisfactorily,  since  they  must  remain  intact 
to  sell  to  advantage. 

Having  harvested  the  crop  in  these  lots  without  disturbing  the 
roots,  8  inches  of  sand  was  again  filled  in  above  the  roots  to  force  them 
a  second  time.  Altho  new  growth  developed,  no  marketable  heads 
were  produced.  Instead  of  one  large  head  to  a  root,  a  cluster  of  small 
shoots  of  no  market  value  developed  from  the  peripheral  buds. 

In  Lots  2  and  20  the  heads  of  the  first  crop  were  cut  at  the  base 
in  the  usual  way  except  that  the  roots  were  not  disturbed.  These 
heads,  being  harvested  intact,  were  of  marketable  grade  (Table  3). 
Sand  was  again  filled  in  above  the  roots  and  they  were  forced  a  second 
time.  The  second  growth  consisted  of  a  cluster  of  small  shoots  from 
each  root  and  was  of  no  market  value. 

In  Lots  1  and  22  the  crops  were  harvested  in  the  usual  way  with- 
out disturbing  the  roots.  For  the  second  forcing,  the  roots  were  placed 
in  darkness  under  conditions  suitable  for  producing  barbe-de-capucin. 
The  layer  of  sand  was  not  replaced.  A  light  crop  resulted,  which  was 
satisfactory  for  home  use  but  of  doubtful  market  value  except  where 
barbe-de-capucin  is  desired.  It  would  therefore  seem  useless  to  try  to 
force  the  roots  a  second  time.  The  best-yielding  roots  may  be  kept 
in  a  dormant  condition  after  forcing  and  planted  out  in  the  following 
spring  to  produce  seed.  The  roots  may  also  be  used  for  stock  feeding 
but  may  produce  an  unpleasant  flavor  in  the  milk  if  fed  to  milk  cows. 

Forcing  Roots  in  Field  Not  Practical 

If  Witloof  chicory  roots  could  be  successfully  forced  in  the  field 
where  they  grow,  the  labor  of  digging  and  transplanting  them  to  the 
forcing  beds  would  be  eliminated.  To  determine  the  practicability  of 
such  a  method,  the  roots  in  a  section  of  a  row  in  Lots  27  and  28  were 
left  in  the  ground  and  the  tops  trimmed  off  this  row  2  inches  above 
the  crowns  at  the  time  the  other  roots  were  dug.  Eight-inch  boards 
were  then  stood  on  edge  on  each  side  of  the  row,  with  6  inches  between 
the  boards.  This  space  between  the  boards  and  above  the  crowns  was 
then  filled  with  8  inches  of  sand.  Old  manure  was  heaped  over  the  row 
to  prevent  freezing.  When  ready  for  forcing,  hot  fermenting  manure 
was  heaped  over  the  row.  In  very  cold  weather  about  30  inches  of 
manure  was  needed.  This  enormous  amount  of  manure  used  in 
proportion  to  the  number  of  roots  covered  would  not  be  practicable  on 
a  commercial  scale. 

Lot  28,  consisting  of  15  feet  of  a  row  which  had  been  protected 
from  freezing,  produced  14  extra  fancy  heads  having  an  average  weight 


460  BULLETIN  No.  309  [May, 

of  3.9  ounces  and  11  No.  1  heads  having  an  average  weight  of  2.6 
ounces.  Lot  27,  which  was  not  protected  from  freezing,  was  a  total 
loss. 

In  addition  to  the  extravagant  amount  of  manure  required  to 
force  the  roots  in  the  field,  this  method  required  a  large  amount  of 
labor  to  maintain  the  proper  forcing  temperature.  In  very  cold  weather 
an  extra  amount  of  manure  had  to  be  heaped  over  the  row,  and  when 
the  weather  moderated  the  covering  layer  had  to  be  opened  a  little  to 
prevent  excessive  heating.  Likewise,  hot  spots  in  the  manure  required 
frequent  attention.  Furthermore  it  was  difficult  to  note  the  progress 
of  the  forced  growth,  for  the  rate  of  growth  varied  with  weather  con- 
ditions and  it  was  necessary  to  dig  thru  the  manure  layer  at  frequent 
intervals  to  determine  it. 

Considering  all  of  these  factors,  it  is  evident  that  altho  the  roots 
may  be  forced  in  the  field  without  removing  them  from  the  row,  it  is 
more  practical  to  dig  the  roots  and  force  them  in  a  more  compact  area. 

Sand  Proves  Best  Material  for  Forcing  Cover 

All  the  roots  used  in  the  foregoing  experiments  were  forced  thru 
a  covering  layer  of  sand,  but  in  four  other  lots  different  materials  were 
used  in  place  of  sand  for  comparison,  and  in  four  lots  no  covering  was 
used.  In  each  case  the  roots  were  bedded  in  soil  in  the  usual  way,  the 
difference  being  only  in  the  8-inch  covering  above  the  crowns. 

In  Lots  57  and  58  sawdust  was  used  instead  of  sand  for  the  cov- 
ering layer.  There  were  30  medium-sized  roots  in  each  lot.  No  extra - 
fancy  heads  were  produced  and  only  8  No.  1  heads.  These  had  an 
average  weight  of  2.1  ounces.  Altho  a  quick  growth  occurred  thru  the 
sawdust,  the  low  yield  of  marketable  heads  apparently  was  due  to  the 
fact  that  the  sawdust  was  not  heavy  enough  to  exert  the  pressure 
which  is  needed  to  develop  solid  and  compact  heads.  The  loose,  open 
heads  were  greatly  inferior  to  heads  forced  thru  sand.  A  second  dis- 
advantage of  sawdust  was  that  it  slightly  flavored  the  blanched  leaves. 

In  Lot  59  a  sandy  soil,  made  by  mixing  1  part  of  sand  to  4  parts 
of  loam,  was  used  instead  of  pure  sand  for  the  covering  layer.  The 
30  medium-sized  roots  in  this  lot  produced  12  extra- fancy  heads  hav- 
ing an  average  weight  of  3.2  ounces,  and  9  No.  1  heads  having  an 
average  weight  of  2.4  ounces.  Altho  this  may  be  considered  a  fairly 
satisfactory  yield,  there  was  more  rot  in  this  lot,  and  it  was  more 
difficult  to  dig  out  and  to  clean  the  heads. 

In  Lot  60  muck  soil  was  used  for  the  covering  layer.  It  was 
thought  that  such  a  light,  porous  soil  would  make  a  satisfactory  cov- 
ering layer.  This  lot,  however,  was  a  total  loss  from  rot.  When  the 
origin  and  source  of  muck  soil  (reclaimed  swamp  land)  is  considered, 
it  may  be  expected  that  such  soil  will  often  contain  organisms  that 
will  cause  rot.  Likewise  such  loose,  light  covering  material  can  not 
be  expected  to  produce  a  compact  head. 


1928]  CULTURE  AND  FORCING  OF  WITLOOF  CHICORY  461 

Lots  36,  61,  62,  and  63  were  forced  in  darkness  without  any 
covering  layer  above  the  crown.  These  produced  barbe-de-capucin; 
that  is,  the  growth  consisted  of  loose  clusters  of  long,  slender,  blanched 
leaves,  as  shown  in  A,  Fig.  4.  They  were  similar  in  texture  and  flavor 
to  the  compact  heads  but  much  less  attractive  in  appearance.  Because 
of  such  characteristics  a  market  is  difficult  to  find  for  this  product.  For 
home  use,  however,  the  growing  of  barbe-de-capucin  has  an  ad- 
vantage; the  covering  layer  of  sand  being  omitted,  the  forcing  boxes 
are  easier  to  handle.  If  only  the  larger  leaves  are  picked  off  at  each 
harvest,  a  continuous  growth  may  be  secured  for  several  weeks  from 
the  same  roots. 

For  a  marketable  crop  of  Witloof  chicory,  sand  is  undoubtedly 
the  best  material  for  covering  the  roots  for  forcing. 


CONCLUSIONS 

1.  Witloof  chicory  should  be  sown  about  June  15  in  Illinois  in 
order  to  secure  the  largest  proportion  of  roots  of  best  forcing  size. 

2.  The  roots  do  not  require  a  rest  period  before  being  forced.  They 
can  be  forced  equally  well  when  dug  in  an  active  growing  condition, 
when  dug  and  forced  immediately  after  growth  has  ceased  in  the  fall, 
or  if  kept  dormant  a  few  months. 

3.  Freezing  is  fatal  to  Witloof  chicory  roots.    The  roots  do  not 
freeze  at  28°  F.,  but  at  10°  F.  they  are  killed  by  freezing. 

4.  The  roots  may  be  stored  successfully  for  several  months,  either 
in  outdoor  trenches  or  in  boxes  in  cold  storage  at  a  temperature  suffi- 
ciently low  to  prevent  growth  but  above  the  freezing  temperature.   A 
temperature  between  28°  and  45°  F.  is  satisfactory.  If  stored  too  long 
(five  months  or  more)  they  are  likely,  when  forced,  to  develop  seed 
stalks,  which  make  the  heads  unmarketable. 

5.  Witloof  chicory  roots  are  not  very  exacting  in  regard  to  the 
temperature  for  forcing.  Temperatures  of  55°  to  80°  F.  may  be  used. 
Low  temperatures  result  in  slower  growth,  producing  in  the  same 
period  a  slightly  smaller  head.    The  optimum  forcing  temperature  is 
about  70°  F. 

6.  Medium-sized  roots,  that  is,  roots  with  a  maximum  diameter  of 
1  inch  to  1%  inches,  produce  the  heaviest  yields  of  marketable  heads. 
Large  roots  produce  compound  heads  which  are  unmarketable,  and 
small  roots  produce  small  yields. 

7.  Altho  the  production  of  one  crop  does  not  exhaust  the  food 
material  stored  in  the  roots,  it  seems  impossible  to  secure  additional 
marketable  yields  by  repeating  the  forcing. 


462  BULLETIN  No.  309 

8.  Altho  the  roots  can  be  forced  in  the  field  without  removing 
them  from  the  row,  it  is  more  practical  to  dig  them  and  force  them  in 
a  more  compact  area. 

9.  Sand  makes  the  best  covering  material  thru  which  to  force 
the  growth  to  produce  firm,  compact  heads. 


UNIVERSITY  OF  ILLINOIS-URBANA 


